This invention relates to medical devices and more particularly to locking devices for setting and holding partial vacuums drawn by syringes.
There are several devices known for restraining a syringe plunger in an extended position while a vacuum is held in the syringe barrel in front of the plunger piston. Such devices might include stepped stops on the plunger such as are shown in U.S. Pat. Nos. 3,882,849 and 3,938,505. These stepped stop devices, however, are not capable of a continuous range of partial vacuums but instead provide only discrete vacuum levels corresponding to the steps on the plunger. Devices which can provide continuous ranges of partial vacuums are known, but these typically require a separate moving part such as the cam shown in U.S. Pat. No. 4,386,606. Such moving parts may be relatively difficult to manufacture and to use, and may be less reliable than a device without such an additional moving part. Moreover, all of these prior art devices appear to require that the standard syringe be modified in some way to accept the locking device.